The present invention generally relates to the field of drilling for oil, gas and water. More particularly, the present invention relates to air drilling and an apparatus, system and process for air storage for speeding up and making the air drilling process more efficient.
Air drilling, which is also known as pneumatic percussion drilling is a technique in which gases, usually compressed air or nitrogen, are used in place of conventionally used liquids to cool the drill bit and lift the cuttings of a wellbore. It can be more efficient and inexpensive than conventional drilling. The first recorded use of air drilling was in the early 1860s. A piston-type compressed air mechanical drill bit bored an 8.5-mile-long Mont Cenis Tunnel in the Alps. Air drilling became a popular alternative to rotary drilling in the late 1940s and early 1950s. Because of limited air compression equipment to properly clean the annulus as the well was drilled, air-drilled holes were normally limited to shallow wells (<6000 ft.). But by the late 1970s, air-drilled holes became deeper when larger volume air compressors and high-pressure boosters were developed. The use of high-pressure air compression equipment rose after a downturn of the oil and gas industry in the 1980s because of the development of a high-energy air hammer and diamond-enhanced hammer bits. The hammers and bits greatly increased the rate of penetration and footage in certain air drilling areas as the Appalachian and Arkoma Basins, thus reducing drilling costs in these areas. These new developments also opened the door for deeper air drilling applications by decreasing both the number of bit trips and the need to downsize the hole's diameter from gauge wear. A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid and torque to the drill bit. The term is loosely applied to the assembled collection of the drill pipe, drill collars, tools and drill bit. Tripping is the complete operation of removing the drill string from the wellbore and running it back in the hole. This operation is typically undertaken when the bit (which is the tool used to crush or cut rock during drilling) becomes dull or broken, and no longer drills the rock efficiently. A typical drilling operation of deep oil or gas wells may require numerous trips of the drill string to replace a dull rotary bit for one well.
Because air is the ideal low density drilling medium, air drilling itself provides many advantages. To achieve the best results and greatest economy, several factors must be considered for air drilling. The best conditions for air drilling involve hard, dry formations that produce relatively few formation liquids. Once the formation is completely dry, or the influx of liquids is small enough to be absorbed in the air stream, the drill cuttings return to the surface as dust. The process allows for the immediate and sustained evaluation of hydrocarbons. Other advantages of air drilling are low cost, increased rate of penetration, extended bit life, superior control in cavernous and lost circulation areas, and minimal damage to liquid-sensitive pay zones. The drill string always remains on the bottom when gas is encountered, which is a tremendous advantage in well control. If no gas is in the hole when a trip is made, no gas will be in the hole when the new bit is returned to the bottom. Sometimes holes filled with mud will allow gas to enter the well bore because of reduced hydrostatic pressure, creating well control issues. With air drilling, gas that has already been penetrated will enter the well bore on trips, but the amount of gas is a known quantity that can easily be jetted away from the rig and operating personnel.
In certain types of air drilling known as air rotary drilling, air alone lifts the cuttings from the borehole. A large compressor provides air that is piped to the swivel house connected to the top of the drill pipe. The air, forced down the drill pipe, escapes through small ports at the bottom of the drill bit, thereby lifting the cuttings and cooling the bit. The cuttings are blown out the top of the hole and collect at the surface around the borehole. Another type of air drilling is reverse air drilling. A tremie pipe is inserted inside the drill pip with a check valve on the bottom of the tremie. Once the formation has produced water, reverse air drilling can begin. As drill rods are added, length of tremie pipe are also added until the tremie is submerged. Air is introduced into the tremie which aerates the column of water within the drill rod. The now aerated column is less heavy than the fluid outside the drill pipe. Air-assisted lift is created up the drill pipe, drawing cuttings from the borehole through the bit, ejecting them at the exit hose attached to the top of the swivel and into the holding pond. Once a water bearing formation is reached, there is little chance of contaminants being introduced in to the borehole. Another type of air drilling uses a down hole air hammer for drilling effectively in hard formations. The downhole air hammer is an activated percussive drilling bit which operates in the manner of a jack hammer commonly seen in surface construction.
However, because air is compressible unlike fluids, air must be compressed to provide energy to drill, and because the process of adding another piece of pipe to the well hole (known as making a connections), air drilling loses pressure to the atmosphere, air drilling has issues because as one drills down and needs to add another piece of pipe to continue drilling, called making a connection, air must be bled off to make this new connection. Once the new connection is made, the air from the compressors is sent back down the drill pipes to start the process again. The driller must now wait for enough air pressure and volume to build up to work the air hammer and lift the drill cuttings out of the well bore. The time it takes for the air to build back up results in increases in the drilling cost because during the air pressure build up time, no drilling is occurring. During this wait time, there is not enough air in the well bore to operate drill motors, air hammers and directional tools because they won't operate without proper air pressure. So other problems can occur. During the air drilling process, drill cuttings are lifted up with air. While air pressure and volume is rebuilding to work the air hammer, no drill cuttings are lifted from the well bore. While waiting for the air pressure and volume to build up to work the air hammer, a mud ring can occur, causing the well bore to become packed off or stopped up. This results in hanging up the drill string and causing it to be stuck in the well bore resulting in a very expensive problem for drillers. The chances for the well bore getting stuck in the well hole increase greatly as time passes waiting for the air to build up after a pipe connection has been made. The deeper the well bore is in the well hole the longer it talks to build the air pressure and volume back up.